The invention relates to a method for the production of a ceramic component comprising a cermet body, especially a rod-shaped cermet electrode.
German patent no. DE 4,335,697 C2 discloses such a method, according to which, as a cermet body, a rod-shaped cermet electrode with a convex spherical shape is used, the largest diameter of which is in the center of the ceramic component and/or for which the borehole is provided with a diameter, which varies over the length and which is larger in the outlet regions of the cermet electrode than in the center of the ceramic component. In the outlet regions of the cermet electrode, a diameter difference between the latter and the borehole of between 0.05 and 0.1 mm is specified, whereas in the interior of the ceramic component the cermet electrode is in contact with the borehole wall. The cermet electrode, inserted in the borehole in this manner, is sintered together with the green compact. Under plastic deformation of the materials, the joint is formed at the places of contact between the ceramic component and the cermet electrode. By these means, a joint, which is almost stress-free and highly vacuum tight, is produced between wall of the borehole and the cermet electrode. The method requires a not inconsiderable expense. It is necessary to adhere to very tight tolerances, in order to be able to produce the low-stress but highly vacuum tight joint desired and to avoid rejects.
Furthermore, German patent application no. DE 19,722,728 A1 discloses a composite body and a method for its manufacture, the composite body consisting of a hard metal, cermet or a ceramic substrate body. From a starting powder mixture, a green compact is pre-pressed here, dewaxed and subsequently sintered in a microwave field and coated with a multi-layer coating. While still having open pores, the green compact is heated further and, at a temperature between 600.degree. C. and 1100.degree. C., acted upon with reaction gases and/or solids, which can be sublimed, which are required for the coating. Subsequently, the temperature is increased further and the green compact is consolidated completely by sintering, until finally the coating is applied. A composite produced in this way is said to have improved adhesion of the coating, making it useful particularly as a cutting plate for metal-cutting processing or as a high-temperature material. No prior knowledge is provided by the above about a ceramic component with a cermet body, integrated at least partially in the interior of the ceramic component, nor are those skilled in the art stimulated to produce a ceramic component with an at least partially integrated cermet body.
U.S. Pat. No. 4,769,097 (=DE 37 04 410 A1) discloses a method for fastening a rod or an electrode in a ceramic component, in accordance with which a rod is disposed in a borehole before the sintering. Within the borehole, the rod has stepped or spherical sections and has a coefficient of the thermal expansion, which is higher and than that of the ceramic component. After sintering, the rod, upon cooling, shrinks more in the radial as well as in the axial direction than does the surrounding ceramic component. By these means, the rod is clamped at the sections mentioned against the contacting regions of the ceramic component, being fixed and fastened in the ceramic component in an air-tight manner. As a result of the clamping, not inconsiderable stresses and strains develop in the contacting regions of the ceramic component. These stresses and strains may turn out to be disadvantageous, especially in the case of later force or temperature changes, and lead to cracks and finally to leaks in the joint region between the rod and the ceramic component.